It is well known that alloyed iron articles, which is used herein to include articles made of steel or other iron alloys, corrode easily by the reaction of iron with oxygen to produce ferrous oxide. The exception, of course, are a group of nickel rich iron alloys sometimes referred to as stainless steels. There has accordingly developed a large industry aimed at prevention or control of iron deterioration due to oxidation.
In a broad sense, the industry is currently limited to providing coatings which prevent oxygen from reaching the alloyed iron article although there other proposals have been made in the literature or have been attempted in the past. For example, at one time, an iron alloy was manufactured which produced an adherent iron oxide layer which did not spall off, or if it did, it produced a healing adherent layer in much the same manner that aluminum oxide produces an adherent layer on aluminum thereby making aluminum relatively non-corrodible. It will suffice to say there is considerable room for improvement in making alloyed iron articles less corrodible.
There are many proposals to produce aluminum layers on alloyed iron articles such as found in U.S. Pat. Nos. 1,165,338; 2,759,250; 3,165,823; 3,400,010; 3,415,672; 3,794,511; 3,864,093; 3,909,921; 3,954,512; 3,959,030; 4,036,670; 4,070,210; 4,202,709; 4,454,823; 4,546,051; 4,619,845; 4,655,852 4,657,787; 4,684,447; 4,983,427; 4,987,003; 5,236,788; 5,411,771; 5,960,835; 6,162,509; 6,727,005; 6,913,841; 6,919,543 and 6,929,825.